Recent global increase in multiple rapid intensification of tropical cyclones

The rapid intensification (RI ≥ 30 knots/24-h) of tropical cyclones (TCs) makes TC forecasting difficult, resulting in severe damage to property and life. Forecasting can get even worse if TCs have experienced RI more than once (referred to as "multiple-RI TCs") in their lifetime. On a global scale, the relation between long-term trends of multiple-RI TC frequency and maximum potential intensity (MPI) changes is investigated in this study. During 1981–2020, the frequency of multiple-RI TCs significantly increased at a rate of 1.2 TCs/decade, which was primarily due to the upper phases of TC becoming conducive to RI as MPI increased. Our analysis shows that the frequency of multiple-RI TCs has increased by 82.43% in 2000–2020 compared to that in 1981–2000, whereas the frequency of single RI TCs has increased by only 1.63%. The rise in MPI elevates the initial intensity at which a TC undergoes maximum intensification rate, making post-Tropical Storm stages of TCs conducive to RI. As a result, TCs can undergo RI multiple times even following a weakening before the intensity approaches MPI.


Introduction
The supplementary information file comprises six figures and a table.Fig. S1 illustrates the sample tracks of both single-RI and multiple-RI tropical cyclones utilized in this study.Fig. S2 displays the trends in the occurrence of rapid intensification (RI) and the associated periods for both single-RI and multiple-RI tropical cyclones.Fig. S3 presents the trends and periodic variations in the frequency of single-RI and multiple-RI tropical cyclone events when considering an RI threshold of 35 knots.Fig. S4 presents a similar analysis to Fig. S3 but with a 45-knot RI threshold.Fig. S5 extends the analysis from Fig. S4 to a subset of data from WMO agencies within the IBTrACS dataset, using a 30-knot RI threshold.Finally, Fig. S6 depicts the changes in the environmental conditions between the two study periods.Tabe S1 gives the details about the the differences between the mean 24-hour intensity changes during different intensity stages of TCs for global TCs, RI-TCs and non-RI TCs corresponding the Fig. 1, 2 in the main manuscript.

Figure
Figure S1 showing the tracks of all (a) single-RI TCs and (b) multi-RI TCs used in the present analysis .Tracks are based on TC records from Joint Typhoon Warning Center (JTWC), National

Figure
Figure S2 showing the trends of (a) LMI of single-RI TCs and multiple-RI and (b) RI period of single-RI TCs and multiple-RI TCs.LMI and RI period trends are based on TC records from Joint Typhoon Warning Center (JTWC), National Hurricane Center (NHC) in the IBTrACS dataset.The trends and p-values this figure are calculated using linear regression analysis.The trends and pvalues this figure are calculated using linear regression analysis.The Matplotlib module (version-3.7.1) of python (https://pypi.org/project/matplotlib/) was used to create the figure.

Figure S3 :
Figure S3: Time series and trend of annual frequency for single-RI TCs (in red), multiple-RI TCs (in green), and multiple-RI events (in blue) at the 35 kt threshold during the period 1981-2020.(b) Frequency changes for total RI-TCs and total RI events, single-RI TCs and events, and multiple-RI TCs and events between the periods P1 and P2.Multi-RI and single-RI trends for 35 knot threshold are based on the IBTrACS dataset.The trends and p-values this figure are calculated using linear regression analysis.The Matplotlib module (version-3.7.1) of python (https://pypi.org/project/matplotlib/) was used to create the figure.

Figure S4 :
Figure S4: Time series and trend of annual frequency for single-RI TCs (in red), multiple-RI TCs (in green), and multiple-RI events (in blue) at the 45 kt threshold during the period 1981-2020.(b) Frequency changes for total RI-TCs and total RI events, single-RI TCs and events, and multiple-RI TCs and events between the periods P1 and P2.Multi-RI and single-RI trends for 45 knot threshold are based on the IBTrACS dataset.The trends and p-values this figure are calculated using linear regression analysis.The Matplotlib module (version-3.7.1) of python (https://pypi.org/project/matplotlib/) was used to create the figure.

Figure S5 :
Figure S5: Time series and trend of annual frequency for single-RI TCs (in red), multiple-RI TCs (in green), and multiple-RI events (in blue) for WMO agencies data during the period 1981-2020.(b) Frequency changes for total RI-TCs and total RI events, single-RI TCs and events, and multiple-RI TCs and events between the periods P1 and P2.Multi-RI and single-RI trends are based on the WMO agencies dataset in IBTrACS.The trends and p-values this figure are calculated using linear regression analysis.The Matplotlib module (version-3.7.1) of python (https://pypi.org/project/matplotlib/)wasused to create the figure.

Table S1 -
Differences in the mean 24-hr intensity changes during different intensity stages of TCs corresponding to Figure 1 and Figure 2.